Numerical Investigations On The Mitigation Of The Hangers Of Suspension Bridges By Using Dampers

With the increasement of the span of suspension bridges, the length of their hangers becomes longer and longer. The hangers are prone to large amplitude of oscillation under the actions of wind loading, vibration of the beam or the main cable due to their small dampings, light weights and low frequencies. In this thesis, the efficiency of the dampers attached on the hangers of suspension bridges is studied by means of numerical method, and the main contents are given as follows:(1) The effects of the support stiffness of the dampers, the stiffness of dampers and the flexural stiffness of hangers are carfully studied by means of numerical method. First, the equations governing the systems are established. Second, the discontinuous Dirac Function in governing equations is approximately handled to adapt the Finite Difference Method(FDM) utilizing in this paper, and the equations governing the systems are numerically solved by FDM. The effects of the support stiffness of damper, the damper stiffness and the stiffness of hangers on the dimensionless curve of damping ratio, the realizable maximum damping ratio and its corresponding damping coefficient are investigated in detail. The results show that the realizable maximum damping ratio and its corresponding optimal damping coefficient decreases with the decrease of the damper support stiffness; the realizable maximum damping ratio decreases as its corresponding optimal damping coefficient increases with the increase of the damper stiffness; the realizable maximum damping ratio firstly increased and then decreased and its corresponding optimal damping coefficient increases with the increase of the hanger flexural stiffness.(2)The effect of the dampers attached to parallel-twin-hangers is studied by means of numerical method. First, the equations governing the systems are established. Second, the discontinuous Dirac Function in governing equations is approximately handled to adapt the FDM utilized in this paper, and the equations governing the systems are numerically solved by FDM.The frequency,mode of vibration and damping ratio of the system are studied when one or more dampers are attached to parallel-twin-hangers. The results show that the dampers attached to parallel-twin-hangers can only work on non-synchronization modes.It can change the order of structure modes, increase the frequency of sole ranger, and limit the vibration amplitude, which is equivalent to a rigid spacer as its damper ratio tends to infinity.(3) The effect of the support stiffness of the dampers and the stiffness of dampers on the torsional vibration mode of ranger bundles connected by rigid spacersis analysed by means of finite element software(ANSYS). The finite element model is built to analyse the effects of the support stiffness of damper and the damper stiffness on the dimensionless curve of damping ratio, the realizable maximum damping ratio and its corresponding damping coefficient. The results show that the damping ratio and the support stiffness of damper will reduce the torsional damper ratio of system, and the dimensionless curve of damping coefficient is equivalent to that of sole hanger-damper system...